Segmental abrasive wheel and method of making the same



May 31, 1938. A. BALL ET AL 2,119,412

SEGMENTAL ABRASIVE WHEEL AND METHOD OF MAKING THE SAME Filed Dec. .30, 1935 2 Sheets- Sheet 1 4v 6' INVENTORS.

IALBE .BA

RAYM o c.a NER BY M ATTORNEY.

May 31, 1938. 1 A. 1.. BALL ET AL SEGMENTAL ABRASIVE WHEEL AND METHOD OF MAKING THE SAME Filed Dec. :50, 1935 2-Sheets-Sheet 2 IN VENTORS ALBERT L RAYMOND c BALL BENNER ATTORNEY;

Patented May 31, 1938 UNITED .STATES SEGMENTAL ABRASIVE WHEEL AND METH- OD OF MAKING THE SANIE Albert L. Ball, Lewiston Heights, and Raymond C.

Benner, Niagara Falls, N.

Y., assignors, by

inesne assignments, to The Carborundum Company, Niagara Falls, N. Y., a corporation Delaware Application December 30, 1935, Serial No. 56,709

13 Claims.

This invention relates to segmental abrasive.

wheels and relates more particularly to means for securing a plurality of wheel segments on a rotatable hub or drum.

, It has become customary to make large wheels as well as many intermediate sizes by building them up from a number of segments because of the difficulties involved in manufacturing and using unitary abrasive wheels which are several feet in diameter and which are composed of artificially bonded abrasive. Somewhat smaller segmental wheels are also desirable in certain cases, the wheels for grinding pearl buttons being one example, where operating conditions are such that a non-uniform thermal condition is brought about by excessive heating of the wheel periphery. The monolithic or continuous ring type of structure is easily cracked by such conditions whereas the segmental wheel is not, the smaller abrasive units being capable of resisting these temperature differences. Some of these dimculties are found in the attempts to uniformly compact, dry and handle abrasive masses which may be six feet in diameter and one foot thick such as the wheels used in grinding cutlery, also in uniformly heating and cooling ceramic masses of these sizes without breakage; the monetary loss occasioned by the breakage of one mass weighing several tons is extreme compared to nearly zero loss when manufacturing the same total mass in the form of small units such as segments.

For a number of reasons bonded abrasive articles made with vitrifiable bonds are usually employed. The vitrification temperatures employed-in this art are usually at least 1000" C. and generally as high as 1300 C. The uniform heating and cooling of an abrasive segment whose dhnensionsrare. much smaller than the dimensions of;a completed wheel is much easier to ac-- I sive segments are each formed with one or more grooves in the faces which are to be placed ad"-' jacent the rotatable support, that is in the 'i 5aces complishithan the uniform heating and cooling of an: abrasive wheel combination which has been iting'a large number of such segf wheel can be, made from'abrasive mixescontaining!finely divided silicon carbide or fused alumina, the abrasive grain being bonded;

by meansof aceramic bond or -by means of a heat hardenablesynthetic resin. A ceramic bond which is cured-by being heated to .a vitrifying temperature and. which is carefully cooled through the criticalannealing range has advam' tages for .use in; wet v grinding from the point of view of resistance to the, disintegrating action of adapted to be combined into water. A ceramically bonded abrasive segment has in general, however, a lower coeflicient of thermal expansion than that of the metal supports for the segments and a coefficient of expansion which is less than that of the steel driving shaft. Such differences in thermal expansion have to be considered in view of the variations in temperature to which a wheel is subjected. when shipped to a cold climate, the temperature of a wheel may be as low as -40 Fahrenheit in transit. In the course of operation the wheel may be subjected to temperatures approaching the boiling point of water, that is temperatures more than two hundred degrees higher than possible transit temperatures when the wheel is shipped to a cold climate. Abrasive segments that have been bonded with a synthetic resin have in general a higher coeflicient of thermal expansion than vitrified abrasive segments. Moreover synthetic resins are usually cured at temperatures not exceeding about 300 Fahrenheit.

After the abrasive segments have been made, their mounting on a rotatable support presents serious difficulties, the overcoming of which constitutes the objects of this invention, such as:

1. The assembly of a large number of segments on a rotatable support in one operation. This is desirable from the points of view of accurate segments to the rotatable support and to each other including the formation of perfect seating means for the segments against the support.

4. .Provision for easy removal of an injured segment and replacement with a new segment. According to the present invention, the abra which are opposite to the working surfaces Eif'the the adjacent portions of the rotatable support which may be in'the form of an annular 111i drum. "The grooves maybe formed in "th ments during the moldingfprocess and i during the casting process. 'The groovesi of thesebodies may have a ways will be referred to generally as dovetail grooves. The direction of the grooves described above may be parallel to the axis of rotation of the wheel or they may be inclined at an angle thereto. In the assembly of the parts, the annularhub is laid on a horizontal base with its axis vertical, and the abrasive segments are placed in position on the base in an annular formation with the dovetailgrooves mentioned above opposite to the corresponding grooves in the hub of drum. The dovetail grooves are then filled simultaneously with a hardenable synthetic resin in liquid or plastic form such as a thermally reversible resin, or are filled with metal. The gaps between the segments and the gaps between the segments and the supporting hub may be filled with the same hardenable synthetic resin that is used to fill the grooves in one modification 'of the wheel structure disclosed below. Resilient materials or metals may also be used between the segments or between the segments and the hub.

The methods of assembly of the segments on the hub which have been briefly referred to above are illustrated by means of the accompanying drawings in which:

Fig. 1 shows a horizontal section of the segments of a wheel assembled around a hub and within the barrel of a mold, the section'being taken on the line II of Fig. 2;

Fig. 2 is a vertical section of. the arrangement shown in Fig. 1, the section being taken on two vertical planes which intersect in the axis of the wheel as indicated by the line II--II of Fig. 1;

Fig. 3 is va vertical section of the mold and article taken in the vertical planes used in Fig. 2, but indicating a metal filling in the grooves and joints;

Fig. 4 is a fragmentary section in a plane perpendicular to the axis of an abrasive wheel made in accordance with the present invention, the scale being enlarged as compared with Fig. 1 and the character of the material used for joining the segments to each other and to the hub being of a similar character to that indicated for filling the dovetail grooves in Fig. 1;

Fig. 5 is a view similar to that shown in Fig. 4 but indicating a modification of the materials used in the dovetail grooves and in the various joints;

Fig. 6 is a view similar to that shown in Fig. 4, but indicating the use of metal in the grooves and joints; and

Figure '7 is a fragmentary view taken. in an axial plane and illustrating the construction of a composite key which is used to connect an abrasive segment and the adjacent portion of the supporting drum.

Referring to'the drawings in detail abrasive segments I are assembled on the base of a mold 6 with the outer surfaces of the segments abutting the inner surface of a mold barrel 2. The barrel 2 is attached to the base of the mold 6 by means of screws as indicated in Fig. 2 of the drawings. abrasivesegments. The segments, the barrel, and the hub are so proportioned that spaces 3 are left between the segments when they are assembled and an annular space is left between the hub and the inner faces of the segments. Spacing strips can be used to aid the workman in making the gaps 3 between the segments of the same thickness for each pair of adjacent segments. Spacers may also be used to obtain a uniform gap between the hub and the inner faces of the segments. The segments are also so A hub or drum 4 is placed inside the above the plunger 5 in suflicient amount to fill the grooves I and 9 as well as the gaps between adjacent segments and the gap between the segments and the hub as a result of the pressure to be exerted on the plastic material. A second plunger I0 is placed on top of the thermoplastic material and the mold is mounted between the platens of a hot press such as is used in plastic molding. The plastic material can be, for example, made from a polymerized vinyl acetate 'resin in which part of the acetate groups have been replaced by acetaldehyde or by formaldehyde, such as can be obtained under the trade name Alvar" 15-70 or Formvar 4146. The Alvar resin is made from a vinyl acetate resin which has been polymerized to such an extent that its molar solution in benzol has a viscosity of 15 centipoises at 20 C. and in which 70 per cent of the acetate groups have been replaced by acetaldehyde.

The Formvar resin is made from a vinyl acetate resin in which part of the acetate groups have been replaced by formaldehyde. It is not intended that the invention be limited to this particular material; many others can be used. There are also phenol formaldehyde types of resin which will serve the purpose.

Plastic material of the type which has just been described (preferably in granular or powdered form) is indicated in Fig. 2 as occupying at the beginning of the operation of the press [the space between the two plungers 5 and I 0.

During the operation of the heated press the plastic material is forced through the holes l3 into the grooves 9 and I and thence into the gaps between the segments I and into the gap between the segments and the hub or drum 4. The mold and its contents are then cooled until the material thus pressed into the cavities of the abrasive wheel has hardened, forming a substantially rigid segmental wheel. I

In the arrangement for the assembly of the abrasive segments illustrated in Fig. 3 the holes I3 in the hub 4 are omitted. The procedure is different in some respects from the procedure just described since the keyways (formed by the pairs of dovetail grooves I and 9) and the various gaps betweenthe members ofthe wheel are to be filled with metal by pouring in molten metal.

In practicing this modification of the invention 1 the abrasivesegrnents I are arranged about the inside of the barrel 2 and on the base 6 as before, and the hub 4 is centered with reference to the base 8 and the barrel 2. The assembly of the segments I and of the members 2, 6 and 4 is then heated to about 100 C., after which metal which has been heated to about 100 centigrade degrees above its melting point is poured into the keyways formed by the pairs of dovetail grooves I and 9 and into the gaps between the adjacent segments as well as the gap between the hub 4 and the segments. While the molten material is being cast into place the entire assembly is jolted or jarred several times by lifting it an inch or two and allowing it to drop; or by striking suitable After cooling blows with a hammer or sledge. the wheel is removed from 1 the oven and is finished by using methods similar to those employed Tellurium 0. 5

Fig. 5 illustrates a form of abrasive wheel of the same general type as that shown in Fig. '4. The oppositely disposed grooves I and 9 (in the abrasive segments and in the hub respectively) are, however, filled with metal, while resilient joints are provided between the abrasive segments and between the segments and the supporting hub. In view of the somewhat more complex character of the mounting in this form of segmental abrasive wheel, a more detailed description is given as an example of a method:

of assembly of the abrasive segments and of the manner in which they are joined to each other and to the supporting hub. 7

Before the segments are brought together, sheets of vulcanizable material are made with the ingredients given in Formula A below.

Formula A Percentage of Constituents composition by Weight Smoked sheet rubber 61. 5 Plasticizer and accelerat 4. 3 Sulphur 28 Ammonium carbonate 6. 2

This composition gives a porous elastic hard rubber on heating to a suitable vulcanization temperature; it is capable of being deformed under pressure such as might result from cooling the assembled wheel and of expanding to fill the joint space upon release of pressure.

The faces of the segments which are to be joined are primed as a preliminary step with a rubber suspension of the type indicated in Formula B. The priming serves to fill the pore spaces in the abrasive and to reinforce the surface against break-down when the abrasive wheel is trued or sharpened. It is customary when using abrasive for certain classes of grinding, etc. to cut a pattern on the working face. This is done with a burring tool which may be provided with either narrow steel cutting edges or steel points; in some instances the wheel face is simply hacked with a steel tool. It is obvious therefore that abrasive corners at joints must be reinforced in order not to chip away excessively.

Formula B Percentage of Constituents composition I 0 by weight Smoked shee't rubber. H. 66 Plasticizer and accelerator 4. 4 Sulphur 29.6

v the wheel while the assembly is still hot.

These constituents are mixed with about eight times their weight of benzol.

The abrasive surfaces to be joined are primed with suspension made as just described and the benzol allowed to evaporate. Where a joint thickness of 3 inch is contemplated for the finished wheel, rubber sheets having a thickness of about tin" and having the constituents of Formula A are prepared. These sheets are cut to size and applied to the primed faces of the segments. The hub or rotatable support for the segments is laid on a base plate with the axis of the hub in a vertical position, a mat of sponge rubber about A" thick being interposed between the hub and the base plate as a sealing means between the two'. A rubber suspension (made up according to Formula B) is brushed between adjacent dovetails on the peripheral surface of the hub which is to be joined to the segments. This priming coating need not be continuous between the dovetail grooves but should be put on midway between the edges of the grooves as openings. After the benzol has evaporated, narrow strips of the rubber sheet mentioned above are applied to the brushed surfaces of the hub.

The abrasive segments are then placed around,

the hub, spacers having a thickness of i being used to obta n this distance between the adjacent segments and the hub. The strips of rubber sheet at this stage of the assembly extend only half way across the 36, inch gaps. A band or hands are placed around the ring of segments to hold them securely in position with respect to each other and with respect to the hub which they enclose. If additional abrasive annuli are to be added, i. e. superimposed upon the first annulus, the horizontal abrasive surfaces which are to be adjacent are primed with the solution given by Formula B andbenzol, and fitted with sheets prepared according to Formula A. Spacer strips are placed on the upper surface of the in a narrow strip extending parallel to the groove first annulus and. the remaining annular rows of segments are built up in a manner similar to that described above in detail for the first annulus. The joints between the annuli are thus formed of the same materials and in the same manner as the joints between segments. The dovetail grooves in the various segments are placed in each case directly opposite to the corresponding grooves in the hub. Where it is desired to stagger the segments in adjacent annuli ample, the article may be heated up at the rate of 25, degrees an hour to 300 F; and held at that temperature for 12 hours. During the curing process the gas forming material in the, rubber strips causes them to swell so that they extend across the gaps between segments and across the gaps between the hub and the adjacent segments. The-dovetail grooves in the hub and the corresponding grooves in the adjacent segments remain connected so that they can be filled with molten metal poured in from the upper side of The cured rubber strips form seals on each side of the keyways so that the metal fills substantially only a series of keyways extending from one side of the wheel to the other and forms a perfectly fitting supporting surface of metal between the base of each segment and the hub surface.

As a further modification of this segmental abrasive wheel having metal keys and resilient joints, the dovetail keys or bars may be provided with resilient interruptions at relatively short intervals along the length of each dovetail bar for the purpose of localizing stresses which may be set up along the length of the assembly due to the diiferential expansion of the various parts.

This can be done for example by partially fillirrg the dovetails with metal, then interrupting the pour to insert short spacers of cured resilient or porous rubber, just above the cast metal surfaces in the keyways. This step-is followed by pouring more metal in the keyways, and if necessary additional cured rubber spacers may be introduced at the desired intervals, until the keyways are completely cast. This type of key is illustrated in Figure 7 which shows a composite key lying between a metal support on the left and an abrasive segment on the right. This composite key is shown as being formed of metal keys interrupted by porous rubber connecting elements.

The rubber strips formed from the ingredients given in Formula A above vulcanize into porous elastic hard rubber joints. The principal purpose of these joints is to balance differences in thermal expansion between the abrasive and the supporting hub.

Another example of joint materials which have been found to serve the purposes of this invention as illustrated in Figure 5 are given in Formulae C and D. Formula C represents a mixture for filling pores in abrasive which when hardened serves to reinforce the abrasive surface to prevent chipping during wheel truing and so oh as described earlier in this specification. Formula D represents a rubber mixture which can be sheeted, cut and applied to surfaces to be joined. When cured the sheets have suitable compressibility to relieve stresses in the assembled wheel.

Formula C Parts by weight rubber 40% clay 10% 50 Water 50% Powdered sulphur 20 This mixture is of easily spreadable consistency and is readily rubbed into the pores of an abrasive surface. It is suitably hardened by heating 8 to 10 hours at 175 F., raising the temperature at 40 F. per hour to 287 F. and maintaining the tempera- Water dispersed rubber containing.

These constituents are milled and sheeted in the customary manner for blending rubber compounds, and are cured after being placed in the desired locations in the assembly by raising the temperature at the rate of 40 F. per hour to 287 F. and maintaining this latter temperature for 90 minutes.

' A segmental abrasive wheel utilizing Formulae C and D is formed substantially in the manner described for the use of Formulae A and B, the

difference for the modification under discussion being that Formula D is sheeted to 2" thickness and thus fills the joint spaces, and the use of shims or solid spacers is omitted, the segments being held in position by bands as before. When the temperature of the joint material is approximately 250 it is soft and the bands are tightened just sufficiently to cause it to fill completely the joint space volume it is intended to occupy. and then the cure is continued to completion. A further modification may also be resorted to when utilizing this invention for joining abra sive segments to a rotatable support. The highl resilient nature of the joints as given by the sheeted materials disclosed in either Formula or D may be substituted by a less resilient structure as produced by the use of a joint material which is heat hardenable at approximately 300 F. but which is heatdisintegrable when the temperature is increased several hundred degrees beyond 300 F. An example of an easily applied joint material possessing these properties is:

It will be found that a cement according to Formula E is of mortar-like, readily spreadable consistency, that it can be rubbed into the porous surfaces of abrasive segments for surface reinforcement, trowelled on to the surfaces in such.

thicknesses that are necessary to form jointsifrom 3%" to 1%" thick if necessary), and furthermore that it has nearly the same coeihcient of thermal expansion as a vitrified bonded fused alumina abrasive; by slightly altering the ratio of resin to filler, cements of different coefficients of expansion can be obtained to agree closely with a particular abrasive selected for use.

The procedure for making a segmental wheel,

patterned alongthe lines shown in Fig. 5 in which the joint materialbetween adjacent abrasive surfaces is to be of Formula E, is as follows, omitting for the sake of brevity those preparatory steps which have been already taught by this disclosure:

1. Apply'joint cement per Formula E to abrasive surfaces which are to be adjacent, leaving a moderate excess of cement upon the surfaces so that when segments are brought together in the desired alignment the excess material may be forced out leaving the joint thickness (1. e. 3 desired.

2. Form the segments to which cement has been applied into. an annulus; light blows with a rawhide hammer upon the ends of segments will serve to force the segments into the desired locations and simultaneously force out any excess joint cement. Fasten a steel retaining-band in position.

3. Harden the joint cement by heating at theannulus, heat the assembly to approximately 300 F., pour the dovetails full of molten metal such as that represented by-Formula N, and jar or jolt the assembly as previously described.

In those cases in which the jointing and key materials which are utilized in carrying out this invention are of a fusible or softenable or disin tegrable nature, as compared to the abrasive and hub which they serve to unite,'the replacement of defective segments is much facilitated. The assembly process to form an integral wheel unit from a support and abrasive segments is inexpensive while the support and abrasive segments are expensive. It is therefore both possible and economical to replace a defective segment or segments, the procedure being simply to heat the wheel to such a degree that the joining materials soften or disintegrate sufliciently to permit gently disassembling it. Obviously, the softening, disintegrating or melting points of the materials used are selected to be safely in excess of any contemplated operating temperatures. The defective segments are replaced by acceptable new segments and the Wheel'reassembled.

Various changes may be made in the materials used in forming the joints and keys of the abrasive wheel without departing from the invention, which is defined within the compass of the following claims.

We claim:

1, An abrasive wheel comprising a plurality of abrasive segments mounted on a rotatable hub, grooves in the outer surf-ace of the hub adjacent the segments, corresponding grooves in the inner surfaces of the segments disposed approximately opposite said grooves in the hub, a metal filling the keyways formed by pairs of oppositely disposed grooves, and strips of resilient material consisting of porous rubber vulcanized to a plurality of the surfaces separatedby narrow gaps to join adjacent segments and to join the hub to the segments across the gaps situated between the keys.

2. An abrasive wheel comprising a plurality of abrasive segments mounted on a rotatable hub, grooves in the outer surface of the hub adjacent the segments, corresponding grooves in the inner surfaces of the segments disposed approximately opposite to said grooves in the hub to form a plurality of keyways, a filling of metal interspersed with connections of resilient rubber in one or more of said keyways and metal fillings in the remaining keyways, and strips of resilient rubber vulcanized in situ to join adjacent segments to each other and to join the hub to' the segments at positions between the keys.

3. The method of making a segmental abrasive wheel which comprises priming the segmental surfaces to be joined to each other and to a rotatable hub with a suspension of rubber and vulcanizer in a liquid, vaporizing the liquid and applying strips of sheet rubber containing vulcanizing material and a gas forming material to the primed surfaces of the segments, assembling the segments around a rotatable hub in such positions that dovetail grooves in adjacent surfaces of the hub and segments come approximately opposite to one another to form keyways between the hub and the segments, heating the assembled segments and the hub to a temperature which will cause the rubber strips to expand and bridge the gaps between the segments and between the segments and the hub and filling the keyways abrasive segments mounted on a rotatable hub, grooves in the outer surface of the hub adjacent the segments and extending parallel to the axis of the hub, corresponding grooves in the inner surfaces of the segments disposed approximately opposite to said grooves in the hub, a filling of mechanically strong resinous material in the keyways formed by pairs of oppositely disposed grooves, and strips of resilient rubber vulcanized in situ to join adjacent segments and to join the hub to the segments across the gaps situated between the keys.

5. The steps in the method of making a segmental abrasive wheel which comprise coating the segmental surfaces to be joined with a heat hardenable material, hardening the coating to substantially its final condition, preparing sheets of hardenable material of approximately the thickness of the joints which they are to fill, assembling the segments around a hub with said sheets distributed in the joint spaces, heating the assembly to soften the sheets, pressing the segments toward each other and toward the hub until the joint spaces are substantially filled with said material, and'raising the temperature of the assembly to complete the cure of the joint material.

6. The steps in the method of making a segmental abrasive wheel which comprise coating the segmental surfaces which are to be joined to each other and to the supporting hub with a,

mixture of water dispersed rubber and vulcanizing agent, vulcanizing the coating on said segmental surfaces, forming rubber sheets for filling the joint spaces by incorporating a vulcaniz-' ing agent into smoked sheet rubber, assembling the segments around a hub with said sheets distributed between the surfaces to be joined, heating the assembly to the softening point of the sheet rubber, pressing the segments toward each other andthe hub until the softened rubber fills the joint spaces, and completing the vulcanization of the rubber in the joints.

7. In a segmental abrasive wheel reinforced joints between abrasive segments comprising layers of heat hardened material'filling the pores 'in the rough surfaces adjacent joint spaces, and

bridges of tough resilient material extending across said joint spaces and attached to saidhard surface layers.

8. In a segmental abrasive wheel reinforced joints between abrasive segments comprising layers of heat hardened material filling the. pores of the rough surfaces adjacent joint spaces, and bridges of porous resilient material extending across saidjoint spaces and attached to said hardened surface layers.

9. An abrasive wheel comprising a plurality of abrasive segmentsjmounted on a rotatable hub, grooves in the outer surface of the hub adjacent the segments and extending parallel to the axis of the hub, corresponding grooves in the inner surfaces of the segments approximately opposite to said grooves in the hub, a filling of metal in the keyways formed by pairs of oppositely disposed grooves, and strips of resilient rubber vulcanized in situ to join adjacent segments and to join the hub to the segments across the gaps situated between the keys.

10. In a segmental abrasive wheel reinforced joints between abrasive segments comprising relatively thin layers of tough non-resilient material filling the pores in the rough surfaces adjacent joint spaces, and bridges of tough resilient material extending across said joint spaces and attached to said tough surface layers.

11. An abrasive wheel comprising a rotatable support, a plurality of abrasive segments mounted on the peripheral surface of said support, and a plurality of keys formed of hard thermoplastic resin interconnecting each of said segments and said rotatable support.

12. The steps in the method of making a segmental wheel which comprise coating with a heat-hardenable material the segmental surfaces to be joined, hardening the coating to substantially its final condition, assembling the segments around a hub with small gaps between adjacent segments and at least partially filling said gaps with a heat-hardenable material, pressing the segments toward each other and toward the hub until said gaps are substantially filled with the intersegmental material, and raising the tempergrooves, bridges of tough resilient material joining the hub to the segments across the gaps that are located between the keyways, and similar bridges between adjacent segments.

ALBERT L. BALL. RAYMOND BENNER. 

